* add /me handling
* use typeguards to avoid fighting TS
* improve clarity and use of typeguards
* add createMessageContent tests
* remove completed TODO
* improve comments
* remove duplication and renaming of argument
* allows switching between modes that retains formatting
* updates rich text composer dependency to 0.13.0 (@matrix-org/matrix-wysiwyg)
* improves handling of enter keypresses when ctrlEnterTosend setting is true in plain text editor
* changes the message event content when using the new editor
* adds tests for the changes to the plain text editor